It's probably a good idea in a high school classroom to lay out your bathroom policy at the beginning of class. In sub situations when I was in HS, lots of students took advantage of the sub's permission to use the bathroom, and they were inconsistent by giving permission to everyone for the first half of class and no one during the second half. Really annoying if someone actually has to go.
long ago when I was a sub I let them go one at a time...worked great, especially the one time when someone left and didn't come back for about 30 minutes, and these two girls really had to go...kept saying "you can go as soon as the first guy comes back..." When he finally came back, they had completely directed their anger towards him instead of me...and then I let them go to the bathroom - one at a time...
I still keep the one out at a time policy to this day as a regular teacher...has worked extremely well for me.
In the district where I live, there was a major issue with a teacher not allowing an elementary student to go to the restroom. All of the elementary teachers now allow students to go both to the restroom and nurse whenever they ask.
Big difference from when I was in school. I think I asked to go to the restroom and nurse a total of about 5 times from K-12.
I totally understand your dilemma because it's something that anyone who's subbed would know. With HS in particular, it's hard to know. Because policy dictates a certain way of doing things (i.e. no unnecessary trips). However, the reality is that many many HS teachers don't follow that rule. In fact, in my experience, lots of HS teachers operate as if they are some adjunct to the school... In other words, they act like an 400 gorilla, and make their own rules with regard to this kind of stuff.
I've subbed in many a room, where S.O.P. seemed to be kids walking in and out, went in teacher's desk, etc. (Again, one can tell if it's something their trying to take advantage of a sub, or if it's routine).
And as a sub, you don't really want to come in and be a stickler on rules with students, when the regular program isn't that way. Normally, if they come up to me and ask me to go somewhere, I'll ask them, "what is your teacher's rules on leaving the room." In lower grades, there tends to be some sort of sign-out sheet sort of deal. At the HS level, I've been in classes where they're required to hit a timer, come back, and whatever amount of time they were gone--they would have to pick the required set of weights up, and do some curls!
Whatever the rules seem to be, I go with it. I do basically the one student at a time rule, unless the class required them to be out of class to do stuff (i.e. journalism). In that case, I'll have them sign in and out on a sign-out sheet of my own.
I think teachers need to include this kind of information in the lesson plans. I have a 2 page "procedures" typed up, and it has EVERYTHING there is to know. Then when I'm out, I just have to type up the plans for that day.
I can always add or change things on the procedures page.
I think if the regular teacher has something like this, a lot of problems can be eliminated.
It is also up to the sub to make sure he/she reads it.
In my procedures I have students collect folders - it's a small classroom, I don't want to be walking around, that close to my students. She ignored this procedure, collected the folders herself, and a guy grabbed her butt.!! There is no excuse for that, but if she followed my instruction, this wouldn't have happened.
The high school I attended (and later subbed in) had a school-wide bathroom policy. I'm pretty surprised to hear that is not normal.
Our agendas had a 'pass' section. There were two slots per class, per marking period. So, you had to use them wisely. This counted for bathrooms, lockers, office, counselor, library, etc... Once you used that quarter's passes in a particular class, you were done. You could beg a friend to use theirs (this was common and not monitored much). Honestly most students abuse this. I probably used about 5-10 passes per YEAR (6 classes x 2 passes x 4 quarters = 48 possible passes), and this included when I forgot something in my locker and had to go back.